Friction welding process and shielding gas shower for carrying out the process

ABSTRACT

The invention relates to a friction welding process for mounting blades of a blade carrier ( 1 ) of a flow machine as well as a shielding gas shower for supplying gas to welding surfaces. To achieve this, a plurality of longitudinally extending welding surfaces ( 5   a ) are provided on the circumference of the blade carrier ( 1 ), are oriented at a blade angle β relative to the rotation axis (R) of the blade carrier ( 1 ), and are respectively welded together with a welding surface ( 5   b ) of a blade ( 2 ). The welding temperature necessary for joining the bodies (blade carrier ( 1 ), blade ( 2 )) is achieved by pressing together the welding surfaces ( 5   a,b ) and simultaneous oscillating relative motion (P) of the bodies ( 1, 2 ) in the welding plane (E), whereby a shielding gas (S) flows around the welding surfaces ( 5   a,b ) during the relative motion (P). The shielding gas flow S follows the contour of the blade carrier and the blade and thus serves to provide a closed shielding gas curtain for protecting the welding surface. In order to ensure a gas supply to the welding surfaces from all sides to the extent possible during the relative motion, the shielding gas shower, which is stationary relative to one of the bodies, comprises a gas outlet opening facing the welding surfaces.

The invention relates to a friction welding process according to the preamble of patent claim 1, as well as a shielding gas shower for carrying out the process according to claim 6. Such a friction welding process is disclosed in EP 513,669 B1.

Such friction welding processes serve for mounting the blades of a blade carrier of a flow machine, for example of entire disks (blisk) or a drum for a jet engine. The blade carrier comprises a conical or cylindrical contour, on the circumference of which a plurality of uniformly mutually spaced blades are welded by means of their blade roots. Both the circumference of the blade carrier as well as the blade root comprise a plane or slightly curved welding surface, and are pressed together by means of an upsetting compressing force in order to develop the necessary welding temperature, so that the area of the welding surfaces is heated to the welding temperature during the translational pendular motion of the blades relative to the blade carrier. The pendular motion is carried out perpendicularly to the longitudinally extending configured welding surface, and can amount to several millimeters in this context.

The friction welding process, which belongs to the class of pressure welding or plastic welding processes, distinguishes itself relative to typical gas or arc melt welding processes by a substantial insensitivity with respect to oxidation in the surrounding ambient air, because, due to the relative motion of the parts to be welded, firstly the access of surrounding ambient air is hindered, and secondly oxides are transported together with the molten material out of the weld zone due to the rubbing frictional motion. Nonetheless, defects have been discovered in the edge and corner areas in the weld seam due to oxide formation. Since such defects reduce the strength of the weld seam, the danger of a blade rupture exists during operation of the flow machine due to the high centrifugal forces.

Beginning from this background, it is an object of the invention to provide a friction welding process of the general type described above for mounting the blades of a blade carrier, which ensures a defect-free welded junction between the blade carrier and the blades. Moreover, a shielding gas shower of the general type described above is to be provided such that it can be employed for carrying out a friction welding process without hindering the relative motion between the bodies that are to be joined.

With regard to the process, the object is achieved according to the invention by means of the characterizing features of patent claim 1.

In contrast to the known rotational friction welding processes, in the welding process of the general type described above using an oscillating relative motion, it cannot be avoided that areas of the welding surfaces corresponding to the amplitude of the relative motion are exposed, and the exposed welding surface is subjected to oxidation due to access by air. In this context, the invention has the advantage that, due to the flowing of a shielding gas around the welding surfaces, these surfaces are surrounded by a shielding gas curtain, so that these are protected against access by air during their relative motion. Due to the fact that the blade and blade carrier form a flow grating, the surrounding flow of the shielding gas effectuates a similar flow field or pattern as occurs during operation of the blade carrier. In other words, the shielding gas flow follows the contour of the blade carrier and of the blade and thus serves to provide a closed shielding gas curtain for protecting the welding surface. Thus, no further measures are needed for maintaining the flow in the area of the welding surfaces, even during the relative motion of the bodies.

In this context it is advantageous to orient the welding surfaces, which are provided with an over-dimension relative to the finished part contours, at the blade angle β and taper angle α, so that the shielding gas flow that develops has a flow that lies against the hub area of the flow machine for as long as possible, similarly as in the case of operating the flow machine, whereby the welding surfaces remain covered by shielding gas. This effect is further reinforced in that the shielding gas flow encompasses at least that area passed over by the moving welding surface, which is made possible by corresponding expansion of the shielding gas flow in the direction of the pendular motion. By correspondingly orienting the shielding gas flow with respect to the taper angle α of the blade carrier and the angle of incidence β of the welding surfaces, a largely adherent or contacting shielding gas flow is achieved in the area of the welding surfaces. In order to ensure a shielding gas supply with the minimum possible interference on the one hand, and the operation of the friction welding process without interference on the other hand, the direction of the shielding gas flow is oriented transverse or perpendicularly to the direction of the relative motion, whereby the relative motion carries out an essentially translational or slightly arc-shaped motion.

The object of the invention relating to the shielding gas shower is achieved according to the invention by means of the characterizing features of patent claim 6.

In order to achieve a supply of gas to the welding surfaces from all sides to the extent possible during the relative motion, the shielding gas shower, which is stationary relative to one of the bodies, comprises a gas outlet opening facing the welding surfaces. The expansion of the gas outlet opening in the motion direction has the advantage for the invention that the area passed over by the moving welding surface is gasable, i.e. can have gas supplied thereto, without gaps, and thus air access to the oxidation sensitive welding surfaces can be prevented. By means of the stationary construction of the shielding gas shower, firstly a defined area passed over by the shielding gas is achieved, and secondly the supply of the shielding gas to the shielding gas shower is simplified.

The arrangement of the shielding gas shower with a spacing perpendicular to the motion direction allows the friction welding process to be carried out unhindered, so that the geometrical motion sequences generally can be maintained. Also thereby, it becomes possible to achieve a gas showering of the welding surfaces that comes close to the actual flow conditions, so that the above initially mentioned advantages with regard to the flow guidance can optimally be ensured, especially since this makes it possible to achieve the gas outlet that is optimal for the flow guidance transversely or perpendicularly to the motion direction.

In an advantageous manner, the shielding gas shower is embodied corresponding to the contour of one of the bodies in the area of the welding surface. Generally, the shielding gas shower is mounted on the blade carrier that is stationary during the friction welding process, so that the shielding gas shower is embodied with an arc-shape corresponding to the cylindrical contour of the blade carrier. Thereby, the shielding gas shower can be mounted surfacially on the disk carrier, so that the access of air between the disk carrier and the shielding gas shower, and therewith an all too intensive mixing with the shielding gas in the area of the welding surfaces, can be prevented.

Further advantageous embodiments of the invention with regard to uniform distribution of the shielding gas over the outlet opening, are achieved by the features of patent claims 11 to 13.

A preferred embodiment of the invention will be described below with reference to the accompanying drawings, wherein:

FIG. 1 shows a partial view of a rotor disk for a flow machine with a mounted shielding gas shower;

FIG. 2 shows a view of the bladed disk along the section line I—I;

FIG. 3a shows a side view of the sectioned shielding gas shower;

FIG. 3b shows a cross-section through the shielding gas shower along the section line II—II in FIG. 3A; and

FIG. 3c shows a sectioned top plan view of the shielding gas shower.

FIGS. 1 and 2 relate to the blade arrangement of a rotor disk for a flow machine such as a jet engine. The rotor disk comprises a blade carrier 1 embodied as a disk onto which a number of similar blades 2 are frictionally welded. The blade carrier 1 and the blades 2 are prepared of a titanium alloy. After the blades 2 or the blade raw blanks are frictionally welded onto the blade carrier 1, the blade roots are subjected to a finishing operation in which material is removed in order to give the blades 2 the final form. A typical blade 2 for axially constructed flow machines comprises a blade vane 3 and a blade root 4, which terminates in a flat planar welding surface 5 a in the raw unfinished condition. The blade vane 3 is relatively long and thin in the radial direction, and comprises a curved form, whereby one major surface of the blade is concave and the other major surface of the blade is convex. The welding surface 5 a as seen in a plan view comprises a contour that is similar to that of the blade profile. The quadratic block-shaped blade root adjoins the blade vane. The welding surface 5 a is spaced by a few millimeters, approximately 2 to 8 mm, from the rest of the quadratic block-shaped part of the blade root 4 by means of a pedestal. During the friction welding, pendular, clamping, and compressive upsetting forces are applied via the blade root 4 onto the blade 2 or the welding surface 5 a.

The blade carrier 1 comprises essentially planar, mutually parallel end faces 6 a and 6 b having a circular shaped plan view. The essentially rotationally symmetrically configured blade carrier 1 comprises a rotation axis R that corresponds to the rotation axis of the flow machine. The end faces 6 a and 6 b extend perpendicularly to the rotation axis R. The circumferential surface 7 of the blade carrier 1 extends between the outer edges of the end faces 6 a and 6 b.

A plurality of slightly protruding webs is formed on the circumferential surface 7. Each web is machined to a planar welding surface 5 b, of which the contour essentially corresponds to the welding surface 5 a of the blade 2. As can be seen in FIG. 1, the longitudinal axis L of each welding surface 5 b is tilted by the blade angle β relative to a straight line parallel to the rotation axis R. The longitudinal axis L of a welding surface 5 b essentially corresponds to the projected chord line of the blade root profile.

In practice, most blade carriers 1 are so configured that the circumferential surface 7 comprises a configuration corresponding to that of a conical-section. As can be seen in FIG. 2, the welding surfaces 5 b or the blades 2 are mounted on the conical-section shaped section of the circumferential surface 7. A cylindrical section of the circumferential surface 7 adjoins the conical-section shaped section. The conical-section shaped section comprises a taper angle α relative to the cylindrical section.

For the friction welding process, the blade carrier 1 is secured in a position in such a manner that the welding surface 5 b to be provided with blades lies in a plane E, which extends parallel to the direction P of the translational pendular motion. The welding surface 5 b to be provided with blades thus is located in the so-called welding position. As can be seen in FIG. 1, the direction P of the pendular motion P, which the blade 2 carries out relative to the blade carrier 1, extends perpendicularly to the rotor axis R, while in FIG. 2 the direction of the pendular motion P is to be imagined as perpendicular to the drawing plane. During the friction welding of a blade 2 onto the blade carrier 1, the welding surface 5 a of the blade 2 is brought into contact with the associated welding surface 5 b of the blade carrier 1, as can be seen in FIG. 2. In order to develop the necessary welding temperature, a compressive upsetting force is applied to the blade 2 perpendicularly to the welding surfaces 5 a,b, and simultaneously the blade 2 is moved rapidly back and forth relative to the blade carrier 1, so that friction heating is developed. If sufficient heat is developed, the pendular motion is discontinued and the compressive upsetting force is maintained, until the blade 2 is finally welded and connected to the blade carrier 1. Next, the blade carrier 1 is released and rotated into a position in which a further blade 2 can be welded on. This sequence is repeated until all blades 2 are welded onto the blade carrier 1.

The blade raw blanks are next subjected to a forming process, in which material is removed from each blade root 4, in order to achieve exactly the desired blade form. The forming process can be carried out both by chip removal as well as electrochemically.

The welding surfaces 5 a′ and 5 a″ shown by dashed lines in FIG. 1 indicate the extreme positions or the amplitude of the blade-side welding surface 5 a, which this blade-side welding surface 5 a carries out during the pendular motion or relative motion P with respect to the carrier-side welding surface 5 b. In this context, the blade-side welding surface 5 a passes over an area of which the largest dimension measures b in the direction of the pendular motion, that is to say perpendicularly to the rotor axis R. In this illustration it is made clear that the welding surfaces 5 a,5 b are temporarily only partly surfacially in contact with one another during the friction welding motion, so that the exposed partial surface would be exposed to access by air. This would have as a result, due to the air access, that an undesired oxide formation would take place on the welding surface, especially in the area of the ends or corners of the weld surfaces. In order to prevent this oxidation, which principally does not arise in the typical friction welding process, a gas showering of the weld surfaces 5 a,5 b by means of a shielding gas flow S is provided.

A shielding gas shower is mounted on a cylindrical circumferential section of the blade carrier 1 for the supply of the shielding gas. The shielding gas shower 8 comprises a circular arc-shaped curved gas outlet opening 9, which extends over the arc length l on the circumferential surface 7. The gas outlet opening 9, which extends perpendicularly to the rotor axis R, is spaced in the axial direction from the carrier-side welding surface 5 b, whereby the spacing a is smaller than the dimension b, which designates the extension of the area that is passed over. In order to protect the welding surfaces 5 a, 5 b against air access from all sides, the length l of the gas outlet opening 9 is maintained at least 50% larger than the area b that is passed over by the weld surfaces 5 a. By means of the central arrangement of the gas outlet opening 9 over the area b, it is ensured that even the outer ends of the welding surfaces 5 a, 5 b can be held within a closed shielding gas curtain during their motion. The dimension of the gas outlet opening 9 in the radial direction is also so dimensioned that a sufficient shielding gas curtain is formed, which prevents the entry of air.

The arrangement of the gas outlet opening 9 relative to the flow-impinged welding surfaces 5 a,5 b or the blade 2 enables a gas flow at the blade 2 at the blade angle β, which comes very close to the actual flow conditions during the operation of the flow machine, so that an adherent shielding gas flow S is formed, which sufficiently reduces a mixing with the surrounding ambient air at least in the area of the welding surfaces 5 a, 5 b. As shown by the flow lines S of FIGS. 1 and 2, the flow lines S substantially follow the contour of the blade root 4 in the area of the profiled welding surfaces 5 a,b and the circumferential surface 7 tilted at the angle α.

In order to prevent the entry of air between the shielding gas shower and the circumferential surface 7 with a consequent mixing of the shielding gas with the surrounding ambient air, the shielding gas shower 8 is embodied with an arc-shape as can be seen in FIG. 3c, so that its radially inner housing wall 10 comes to lie against the circumferential surface 7 in a substantially gap-free manner.

As shown by the FIGS. 3a to 3 c, the shielding gas shower 8 comprises a welded sheet metal housing 11, two pipe conduits 12 a and 12 b for the gas supply, and flow distribution means 13. The two pipe conduits 12 a and 12 b for supplying the gas are connected to the box and circular arc-shaped sheet metal housing 11, whereby respectively one pipe conduit 12 a, 12 b enters into the housing 11 at the end faces 14 a,b of the circumferential ends of the housing wall 10. There, in the housing 11, the pipe conduits 12 a, 12 b extend in a gas chamber 15 to approximately the center of the sheet metal housing 11. The gas chamber 15 and the pipe conduits 12 a, 12 b extending therein are arranged approximately in an upper third in the shielding gas shower 8 on a side opposite the gas outlet opening 9. The pipe conduits 12 a, 12 b are perforated with numerous openings within the gas chamber 15, so that a uniform supply of the shielding gas into the gas chamber is ensured. On an opposite side of the gas chamber 15, the sheet metal housing 11 is opened and thus forms the longitudinally extending arc-shaped gas outlet opening 9. A means 13 for flow distribution, which is formed of many layers, comprising steel wool and filter material, is provided between the gas outlet opening 9 and the gas chamber 15, thus in the bottom half of the shielding gas shower 8. The layers of steel wool and filter material lead to a uniformalization of the shielding gas flow S over the entire gas outlet opening 9.

Two securing bails 17 are mounted on the sheet metal housing 11 for securing the shielding gas shower 8 on the blade carrier 1. 

What is claimed is:
 1. A friction welding process for mounting a blade on a blade carrier of a flow machine, wherein said blade carrier has a circumference and a carrier welding surface provided on said circumference and extending longitudinally oriented at a blade angle β relative to a line extending parallel to a rotation axis of said blade carrier on said circumference, and wherein said blade has a blade welding surface, said process comprising the steps of: a) placing said blade so that said blade welding surface contacts said carrier welding surface; b) orienting said blade on said carrier welding surface so that a longitudinal dimension of a cross-section of said blade extends at said blade angle β; c) moving said blade and said blade carrier in an oscillatory motion relative to each other while contacting and pressing said blade against said blade carrier with a compressive force normal to said blade welding surface so as to frictionally generate a welding temperature sufficient to weld said blade to said blade carrier, wherein respective edge portions of said blade welding surface and said carrier welding surface are intermittently moved out of contact with each other and exposed due to said oscillatory motion; and d) flowing a shielding gas flow concurrently with said step of moving said blade and said blade carrier, while directing said shielding gas flow to flow in a flow direction that corresponds to said blade angle β directly along said intermittently exposed respective edge portions of said welding surfaces and directly along a circumference of said blade carrier to provide a shielded welding area that encompasses said carrier welding surface to which said blade is being welded.
 2. The friction welding process according to claim 1, wherein said oscillatory motion is an essentially translational motion.
 3. The friction welding process according to claim 1, wherein said oscillatory motion is an essentially arc-shaped motion.
 4. The friction welding process according to claim 1, wherein said circumference of said blade carrier includes a conically tapering surface that tapers relative to said rotation axis at a taper angle α, and wherein said step d) comprises directing said shielding gas flow so that said flow direction further corresponds to said taper angle α and said shielding gas flow maintains direct contact along said conically tapering surface.
 5. The friction welding process according to claim 1, wherein said oscillatory motion is carried out over a full excursion distance b that corresponds to a full excursion of a complete motion cycle of said blade relative to said blade carrier in a circumferential direction around said rotation axis, and said shielded welding area has a length dimension l in said circumferential direction that encompasses and is at least as large as said full excursion dimension b, so that said shielded welding area completely encloses said intermittently exposed edge portions of said welding surfaces.
 6. The friction welding process according to claim 5, wherein said length dimension l of said shielded welding area overlaps and is at least 50% larger than said full excursion distance b.
 7. The friction welding process according to claim 1, wherein said step d) comprises directing said shielding gas flow transversely relative to a direction of said oscillatory motion.
 8. A shielding gas apparatus for providing a shielding gas flow for a friction welding process, said apparatus comprising a housing that includes a cylindrically curved solid wall and an annular side and that encloses a gas plenum space therein, and a gas supply conduit connected to said housing and communicating into said gas plenum space, wherein said cylindrically curved solid wall curves along a partial circular arc about a center axis and is oriented facing toward said center axis, wherein said annular side extends over a partial circular annulus along a radial plane perpendicular to said center axis, wherein said annular side has at least one gas outlet opening that communicates out from said gas plenum space and is configured so as to direct a shielding gas flow from said apparatus in the form of a partial cylindrical gas curtain directed parallel to said center axis.
 9. The shielding gas apparatus according to claim 8, wherein said gas supply conduit protrudes into and extends internally along said gas plenum space.
 10. The shielding gas apparatus according to claim 9, wherein said gas supply conduit extending internally along said gas plenum space is perforated with perforation holes adapted to distribute shielding gas into said gas plenum space.
 11. The shielding gas apparatus according to claim 10, wherein said perforation holes are provided only on a side of said gas supply conduit facing away from said annular side of said housing.
 12. The shielding gas apparatus according to claim 8, further comprising a gas distributor arrangement interposed between said gas plenum space and said gas outlet opening.
 13. The shielding gas apparatus according to claim 12, wherein said gas distributor arrangement comprises at least one of steel wool and filter material.
 14. A combination of a shielding gas apparatus, a blade carrier, a blade that is to be frictionally welded onto said blade carrier, and a blade moving device adapted to relatively move said blade and said blade carrier, wherein: said blade carrier is bounded by a circumferential surface that curves circularly about a center axis and that includes a carrier welding surface; said blade includes a blade body and a blade welding surface, which is arranged and pressed into contact with said carrier welding surface; said blade is oriented with a chord line of said blade extending at a blade angle β relative to a straight line parallel to said center axis on said circumferential surface; said blade moving device is adapted to move said blade oscillatingly back-and-forth in an oscillation range (b) in a motion direction tangent to said circumferential surface in a plane perpendicular to said center axis, so as to develop frictional heat in said blade welding surface and said carrier welding surface; said shielding gas apparatus is mounted stationary relative to one of said blade and said blade carrier; said shielding gas apparatus comprises a housing and a gas supply conduit communicating into said housing, wherein said housing has at least one gas outlet opening oriented so as to direct a flow of shielding gas from said apparatus onto said blade in a direction perpendicular to said motion direction; said apparatus is spaced away from said blade perpendicular to said motion direction; and said at least one gas outlet opening extends over an arcuate length (l) parallel to said motion direction, wherein said arcuate length (l) is at least equal to said oscillation range (b), so that said at least one gas outlet opening is adapted to form said flow of shielding gas as a partial cylindrical gas curtain that flows along said circumferential surface around said blade while completely enveloping said oscillation range (b).
 15. The combination according to claim 14, wherein said housing of said apparatus includes an arcuately curved wall that is arranged matingly surfacially contacting said circumferential surface. 